1. Field of the Invention
The present invention relates to a catalytic process for the selective epoxidation of cis double bonds in macrocyclic aliphatic hydrocarbons.
2. Discussion of the Background
Macrocyclic olefins are important building blocks in the synthesis of numerous specialty chemicals. An important representative of such cyclic hydrocarbons is cis,trans,trans-1,5,9-cyclododecatriene, which is formed on an industrial scale by the cyclotrimerization of 1,3-butadiene, preferably on a titanium catalyst, and is used as the precursor for cyclododecanone, dodecanedioc acid and laurolactam/nylon 12.
Numerous processes for the epoxidation of macrocyclic olefins are known. Organic peracids, such as performic acid, peracetic acid or perpropionic acid, can be employed. EP-A-0 033 763 (Degussa AG) describes the reaction of cyclododecatriene (CDT) with performic acid, which is formed in situ from hydrogen peroxide and formic acid. EP-A-0 032 990 (Henkel KGaA, Degussa AG) describes the reaction of derivatives of cyclododecatriene with performic acid. In the case of acid-sensitive olefins, problems arise from side reactions or subsequent reactions which the epoxides can undergo under the acidic reaction conditions. The acid-catalyzed addition of water onto the epoxide results in a vicinal diol; isomerization at the double bonds also occurs.
EP-A 0 055 387 (Peroxid-Chemie) therefore recommends neutralizing the carboxylic acids remaining before the epoxidation as an improvement after the synthesis of the peracid. Besides peracetic acid, perpropionic acid and perbutyric acid are also claimed as oxidants. This process has the disadvantage of large amounts of salt that are formed during the neutralization. The oxidation with other peracids, such as meta-chloroperbenzoic acid (M. D. E. Forbes, J. Phys. Chem. 97 (1993) 3390-3395) is, as already stated in EP-A-0 055 387, uneconomical on an industrial scale.
The epoxidation with a peracid proceeds nonselectively with respect to attack on the cis double bond. W. Stumpf and K. Rombusch (Ann. Chem. 687 (1965) 136-149) were able to show in the systematic study of the reaction of cis,trans,trans-1,5,9-cyclododecatriene with performic acid that one of the two trans double bonds is attacked to the extent of 92% and the cis double bond is attacked to the extent of only 7%. This gives a trans:cis reactivity of 6.5:1. As a consequence, the two trans double bonds of cis,trans,trans-1,5,9-cyclododecatriene are preferentially attacked in the presence of an excess of oxidant, and considerable amounts of diepoxide are formed.
Besides the undesired trans selectivity, it should be noted that on use of organic peracids, large amounts of organic acids are formed and have to be separated from the reaction mixture and worked up. In addition, the use of organic peracids on an industrial scale requires considerable safety efforts, which is also pointed out in EP-A-0 032 990 and EP-A-0 033 763. To date, industrial processes using organic peracids for the epoxidation of cyclododecatriene have not become established.
The difficulties in working up large amounts of organic carboxylic acids can be circumvented if the peracid is replaced by other oxygen sources in combination with catalytic amounts of transition-metal salt as an oxidant.
The transition-metal catalysts used are frequently based on compounds from sub-group 6 of the Periodic Table, in particular on tungsten and molybdenum. These transition metals are preferably employed in the form of their polyacids or heteropolyacids or as polyoxometallate anions.
Monoolefins can easily be epoxidized at high conversion rates and yields using such catalysts by means of a large excess of oxidant. Typical monoolefins on which catalyst systems of this type are tested are cyclohexene and cyclooctene. The oxidants used, besides hydrogen peroxide, are also atmospheric oxygen (WO 98/54165, Yissum Research Institute, DD 212960, Akademie der Wissenschaften) and iodosylbenzene or the pentafluorinated derivative (U.S. Pat. No. 4,864,041, Emory University).
In the liquid phase, the reaction can be carried out in one phase or two phases. If two liquid phases are present and the transition metal is used as a homogeneous catalyst, its action is improved by phase-transfer catalysts, typically quaternary ammonium, pyridinium or phosphonium salts.
Processes in which the catalyst is adsorbed onto an inorganic or organic support material are described, for example, in WO 93/00338 (Solvay Interox) and U.S. Pat. No. 5,684,071.
The synthesis is significantly more difficult if, as in the case of cyclododecatriene, only one of a plurality of double bonds in the molecule is to be epoxidized selectively. In the current state of the art, hydrogen peroxide is employed in a large sub-stoichiometric amount, and the reaction must be terminated after relatively low conversions (typically  less than 25%), so that the selectivity of the reaction does not drop below 90%. Based on these teachings, Ube Industries in EP-A-0 950 659 have recently described an industrial process for the synthesis of CDT monoepoxide in which a multistage reactor cascade is operated at from 20xc2x0 C. to 120xc2x0 C.
The catalyst claimed by Ube is the combination of a quaternary ammonium salt or pyridinium salt with a tungsten-containing acid or salts thereof, dodecatungstate, tungsten-containing heteropolyacids or salts thereof. In the examples given, the reaction with sodium tungstate dihydrate (Na2WO4.2 H2O) and tungstophosphoric acid (H3PO4.12WO3.x H2O) described specifically. The latter has the disadvantage that acid-sensitive epoxides undergo subsequent reactions. In addition, the aqueous solution has a highly corrosive action.
In the examples, cyclododecatriene and hydrogen peroxide are employed in the ratio 4:1. At the end of the reactor cascade, from 21.5 to 22.1 mol % of CDT have been reacted, giving a selectivity of monoepoxide of from 91.2 to 94.2 mol %.
In comparison (EP-A-0 950 659, Example 5), Ube quotes the reaction with tungstophosphoric acid on a laboratory scale at a CDT:H2O2 ratio of 5:1, in which 18.2 mol % of CDT are converted into the monoepoxide with a selectivity of 95.0 mol %.
The patent applicant mentions as an advantage of his own process the comparatively high conversion rate and yield. Although the latter, at about 22 mol %, is better than in the comparative example indicated, about 78 mol % of unreacted cyclododecatriene must nevertheless still be separated off during work-up and circulated in this process.
Therefore, it is an object of the present invention to develop a process which is distinguished by the fact that a cis double bond in a macrocyclic olefin is epoxidized as selectively as possible in the presence of at least one further trans double bond with a conversion of greater than 25%.
A further object of the present invention is to find a neutral catalyst system to enable the process also to be employed in the synthesis of acid-labile epoxides.
Surprisingly, it has now been found that both objects are achieved by the use of specific polyoxometallates of molybdenum and of tungsten.
The above and other objects of the present invention have been achieved by a process for the preparation of a macrocyclic monoepoxide containing at least one double bond, comprising:
reacting a macrocyclic aliphatic hydrocarbon containing at least one cis double bond and at least one trans double bond with hydrogen peroxide in two liquid phases in the presence of a homogeneous catalyst system;
wherein said homogeneous catalyst system consists of an oxidation catalyst and a phase-transfer catalyst; and
wherein said oxidation catalyst consists of a) a polyoxometallate of tungsten or molybdenum and b) at least one element from group 14 to 16 of the Periodic Table.